1. Technical Field
The present invention relates to ballast circuits for gas-discharge lamps and in particular a system and method for load balancing between ballasts and improving reliability of lighting systems.
2. Description of Related Art
Gas-discharge lamps include fluorescent lamps, low and high pressure sodium lamps, metal halide lamps and high-intensity discharge (HID) lamps. A high-intensity discharge (HID) lamp produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. The tube is filled with both gas and metal salts. The gas facilitates the arc's initial strike. Once the arc is started, the arc heats and evaporates the metal salts forming a plasma, which greatly increases the intensity of light produced by the arc and reduces its power consumption.
Ballasts are used where an electrical load, e.g. gas-discharge lamp cannot effectively regulate current use such as when a gas discharge lamp presents a negative (differential) resistance to the supply. If a gas-charge lamp were connected to a constant-voltage power supply, the lamp would draw an increasing amount of current until it is destroyed. To prevent this, a ballast provides a positive resistance or reactance that provides current to the gas discharge lamp at an appropriate level.
International patent application publication WO2006109313 of the same applicant discloses a system and method for configuring a single ballast for use with different power ratings and/or different lamp types. The electronic ballast includes hardware typically including a microprocessor to support a large range of output powers, e.g. 20-1000 W, and programmable parameters (or software versions) which support different types of lamps and optional features including a dimming option, and dimming delay. The manufacturer may supply hardware and/or software to a local supplier, reseller, customer or distributor for configuring the ballast. Typically, the distributor requires for configuring the ballast a computer with a connection to a communications port of the ballast. The ballast can be monitored individually or as as part of a group through its communication interface by master control software installed on a computer. Combined with a computer and optional hub, thousands of lamps can be controlled and monitored by authorized site engineers using wired or wireless connection. With the proper security authorization, a site manager can control, dim, and monitor individual and group of lamps from virtually any place on the globe.
The term “synchronization” or “synchronous” as used herein refers to maintaining identical or nearly identical phase and frequency between two or more sinusoidal alternating currents.